Biology and population dynamics of sorghum head bugs (Hemiptera: Miridae)

Abstract

Four mirid head bugs, Calocoris angustatus Leth., Creontiades pallidus Ramb., Eurystylus bellevoyei Put. and Reut., and Campylomma sp., infest sorghum at ICRISAT Centre in India. C. angustatus is the predominant species, followed by Campylomma sp., C. pallidus and E. bellevoyei. The incidence of C. angustatus is higher in crops grown on Vertisols than on Alfisols, and maximum numbers are recorded in panicles at the milk stage. Females of C. angustatus lay eggs inside the glumes before anthesis, whereas the other species insert their eggs in the grain at the milk stage. The life cycle is completed in 15–20, 17–23, 14–16 and 16–17 days by C. angustatus, C. pallidus, E. bellevoyei, and Campylomma sp., respectively. The maximum numbers of C. angustatus, C. pallidus and E. bellevoyei were recorded during September–October, whereas Campylomma sp. tended to be most active during March–June. Lower minimum temperature (<18°C) and relative humidity (r.h.) (<30%) were associated with a decline in C. angustatus density during November–January, while higher temperatures (>32°C) and lower r.h. (<30%) restricted its numbers during March–June. During the rainy season, rainfall, temperature and r.h. were generally positively associated with populations of C. angustatus, C. pallidus and E. bellevoyei. However, there were some exceptions in some years. During the post-rainy season, higher temperatures (>32°C) and moisture deficit had a negative association with numbers of C. angustatus, C. pallidus and E. bellevoyei. However, these factors were positively associated with numbers of Campylomma. Weather parameter means for the same week and two preceding weeks showed a greater effect on C. angustatus populations.